Generally an airframe's maintenance requirements will have specified maintenance intervals for both and also in months, with the maintenance check and part repl

Generally an airframe's maintenance requirements will have specified maintenance intervals for both and also in months, with the maintenance check and part replacements being carried out whichever occurs first. (and different parts are exposed to different types of metal stress. A lot of the most expensive life limited parts are fitted to engines) Fuel consumption, one of the biggest cost disadvantages of older aircraft, is more closely related to hours than cycles